Field of the Invention
The present invention relates to a multiple variable valve lift apparatus. More particularly, the present invention relates to a multiple variable valve lift apparatus which realizes multiple valve lift by a simple structure.
Description of Related Art
Generally, an internal combustion engine receives fuel and air into a combustion chamber and generates power by combusting the fuel and the air. An intake valve is operated by drive of a camshaft, and air flows into the combustion chamber while the intake valve is open. In addition, an exhaust valve is operated by driving of a camshaft, and air is exhausted from the combustion chamber while the exhaust valve is open.
Optimal operation of the intake valve/exhaust valve, however, depends on the RPM of the engine. That is, an appropriate time for lifting or opening/closing the valves depends on the RPM of the engine. In order to implement an appropriate valve operation in accordance with the RPM of the engine, as described above, a VVL (Variable Valve Lift) apparatus that operates valves at different lifts in accordance with the RPM of an engine has been studied.
Meanwhile, in a variable valve lift apparatus having a cam shift type which is configured that a plurality of cams are designed for driving a valve and the plurality of cams is moved along an axial direction, it is important that relative position between the plurality of cams and a valve opening/closing device is exactly controlled.
In case that relative position between the plurality of cams and a valve opening/closing device is not exactly controlled, interference is occurred between elements for guiding axial direction motion of the plurality of cams and the valve opening/closing device or between the plurality of cants and the valve opening/closing device. Thus, the valve opening/closing device or the variable valve lift apparatus may be damaged, or reliability of a cam shift may be deteriorated.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.